Experiment 5 Prelaboratory Assignment Percent Water in a Hydrated Salt Date -lab

Question

Experiment 5 Prelaboratory Assignment Percent Water in a Hydrated Salt Date -lab Sec. Name Desk No.- 1. Calcium chloride, a deliquescent salt, is used as a desiccant in laboratory desiccators to maintain a dry environment. Explain. 15b 2. Experimental Procedure, Part A.1. What is the purpose of firing the crucible? 3. A 1.803-g sample of gypsum, a hydrated salt of calcium sulfate, CasO, is heated at a temperature greater than 170 C in a crucible until a constant mass is reached. The mass of the anhydrous CaSO, salt is 1.426 g Calculate the percent by mass of water in the hydrated calcium sulfate salt. 4·The gravimetric analysis of this experiment is meant to be quantitative; therefore, all precautions should be made to minimize errors in the analysis. a. The crucible and lid are handled exclusively with crucible tongs in the experiment. How does this technique maintain the integrity of the analysis? b. Mass measurements of the crucible, lid, and sample are performed only at room temperature. Why is this technique necessary for a gravimetric analysis? Experiment 5 87

Explanation / Answer

Answer:

1) The purpose of using desiccators is to absorb moisture. Anhydrous Calcium chloride (CaCl2) has a capacity of absorbing moisture as it is hygroscopic in nature, so it is used as a desiccators.

The chemistry behind the dehydration is coordination of water. Anhydrous CaCl2 has no water coordinated, the driving force is the enthalpy of the reaction; CaCl2 + nH2O = CaCl2(H2O)4 delta(Hº= -163 kJ/mol). In addition, the solid Cacl2 is not ionized, but in aqueous solution exist only Ca(aq)++ and Cl(aq)-. The solvation and ionization of the cations, are chemical processes responsible of the heat evolved.

Note: As per chegg gudelines solve first question.

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